The present invention relates to a polytrimethylene terephthalate fiber (hereinafter referred to as PTT fiber), which is a kind of polyester fiber, and a method for producing the same. Specifically, it relates to a so-called two-step method for producing PTT fiber wherein polytrimethylene terephthalate is melt-spun and once taken up as an undrawn fiber after which it is drawn to be the PTT fiber and the PTT fiber thus obtained has a high uniformity suitable for a clothing use. More specifically, it relates an atmospheric condition and a time period for maintaining the undrawn fiber in the above-mentioned method for producing the same.
Polyester fibers mainly composed of polyethylene terephthalate have widely been produced, all over the world, as synthetic fibers most suitable for clothing use, and the polyester fiber industry has already developed into a major industrial field.
On the other hand, PTT fiber has long been studied, but it has not yet reached full-scale industrial production because of a high price of trimethylene glycol which is one of raw materials thereof in the prior art. In this regard, a method has recently been invented, for producing trimethylene glycol at a low cost, whereby there is a possibility of industrialization.
PTT fiber is expected to be an epoch-making fiber having the advantages of polyester fiber and nylon fiber, and the application thereof has been studied for clothing use or carpet use in which the advantages thereof are desirable.
PTT fiber has long been known in the prior art and, for example, from Japanese Unexamined Patent Publications (Kokai) No. 52-5320 (A), No. 52-8123 (B), No. 52-8124 (C), NO. 58-104216 (D), J. Polymer Science: Polymer Physics Edition Vol., 14, 263 to 274 (1976) (E), and Chemical Fibers International Vol., 45, April (1995) 110 to 111 (F).
In these prior arts, PTT fiber is produced by a so-called two-step method and there is the following description in (D) which is technically similar to the present invention:
xe2x80x9cSince PTT undrawn fiber produced by an ordinary production method, i.e., at a spinning rate of lower than 2000 m/min has extremely low degrees of orientation and crystallization and a glass transition point as low as 35xc2x0 C., the properties thereof very quickly change with time whereby it is difficult to obtain PTT fiber having favorable properties because of the generation of fluff or neps during a drawing process.xe2x80x9d
A method is proposed in (D) as a technique for avoiding this problem, wherein a spinning rate is 2000 m/min or higher, preferably 2500 m/min or higher to develop the degrees of orientation and crystallization and a drawing temperature is maintained in a range from 35 to 80xc2x0 C. Also, there is an example in (D) wherein an undrawn fiber obtained at a spinning rate of 3,500 m/min is drawn after being left for 24 hours under the condition of 20xc2x0 C. and 60% RH.
Although there is a description in (D) that the structure and physical properties of the undrawn fiber spun at a spinning rate lower than 2000 m/min significantly vary with time at a room temperature to directly disturb the drawing stability, there are neither descriptions nor suggestions of countermeasure for avoiding adverse effects caused by such a variation with time of the undrawn fiber obtained at a spinning rate of lower than 2000 m/min, not to speak of concrete means for suppressing such variation with time within a minimum limit to obtain a high quality fiber while maintaining a favorable drawing stability.
From the description of Examples in (D), PTT fiber resulted from the method of (D) has a toughness of 18 (cN/dtex)%xc2xd or less, from which it will be apparent that the mechanical property is poorer.
In a comparative example disclosed in (D), a description is seen in that an undrawn fiber spun at a spinning rate of 1200 m/min was left in the atmosphere at 20xc2x0 C. and 60% RH, and thereafter drawn to be a drawn fiber having a toughness of as low as 18 (cN/dtex)%xc2xd, however, there is no description on the variation value of fiber size (U%) or the periodic fluctuation thereof.
As a result of studies according to the present inventors, it was found that when PTT fiber is produced by the two-step method wherein a spinning rate is 1900 m/min or less, a shrinkage of the resultant undrawn fiber varies with atmospheric temperature and time as shown in FIGS. 1 and 2. It was also found that if the variation of shrinkage with time is large, an undrawn fiber package transforms from a normal shape as shown in FIG. 3A to an abnormal shape as shown in FIG. 3B due to the shrinkage as the time lapses, and lengths of the undrawn fiber in the package are partially adhered to each other to disturb the smooth unwinding of the undrawn fiber, which results in the large fluctuation of unwinding tension and the generation of many yarn breakages or single-filament breakages to worsen the drawing stability. Note that, in FIGS. 3A and 3B, reference numeral 1 denotes the undrawn fiber and 2 denotes a bobbin for taking up the undrawn yarn.
Also, it was apparent that the drawn yarn obtained from the undrawn fiber wound in the package transformed due to the variation of shrinkage with time generally has a large variation value of fiber size, i.e., U%, and the periodic fluctuation thereof corresponding to a traverse width of a take-up winder for the undrawn fiber (2 to 5 m as converted to the drawn fiber) or integral times thereof (see FIGS. 4A and 5A). A knit or woven fabric made of such a drawn fiber having the large U% and the periodic fluctuation of fiber size is in general unevenly dyed to exhibit a periodic dyeing speck or luster which is apparently unsuitable for a clothing use in which the uniformity is the most important property.
Generally speaking, in the industrial production of synthetic fiber by the two-step method, maximally three or four days are required for completing the drawing after the undrawn fiber has been taken up, whereby influence of the variation in shrinkage with time is substantially inevitable. Accordingly, the industrial production of PTT fiber suitable for the clothing use is impossible under the condition wherein the variation in shrinkage with time is significant as in the above manner.
An object of the present invention is to provide a high-quality PTT fiber suitable for clothing use obtained by a two-step method, which can be drawn in a stable manner (to result in a high yield), high in toughness and low in variation of fiber size, particularly in periodic fluctuation of fiber size, preferable for an apparel, excellent in quality, and a method for industrially producing such PTT fiber. A problem to be solved by the present invention is to suppress the shrinkage of the undrawn fiber with time as much as possible, to reduce the fluctuation of unwinding tension of the undrawn fiber and to eliminate the adverse effect on the drawing stability of the undrawn fiber and on the quality of the drawn fiber.
As a result of diligent study, the present inventors found the relationship between the atmospheric condition (temperature and relative humidity) in which PTT undrawn fiber is retained and the shrinkage variation of the undrawn fiber with time as well as the relationship between the atmospheric condition and the drawing stability or the quality of the drawn fiber. The present invention has completed based on such a knowledge.
That is, a first aspect of the present invention is a twisted or non-twisted PTT fiber high in uniformity, having an intrinsic viscosity in a range from 0.7 to 1.3, composed of 95 mol % or more of repeated units of trimethylene terephthalate and 5 mol % or less of repeated units of other ester, characterized in that a toughness of the fiber is 19 (cN/dtex)%xc2xd or more and a variation value of fiber size (U%) during the continuous measurement of the fiber size by an evenness tester is 1.5 or less as well as the fiber exhibits either one of characteristics defined by the following requisites (1), (2) and (3);
(1) a periodic variation on the smaller fiber size side at an interval of 10 m or less exists in an evenness tester chart, and a magnitude of the variation is 2% or less of an average fineness,
(2) while the existence of the periodic variation on the smaller fiber size side at an interval of 10 m or less is not discernible from the evenness tester chart, a periodic variation at an interval of 10 m or less exists in a diagram for analyzing the period of fiber size variation, and
(3) no periodic variation on the smaller fiber size side at an interval of 10 m or less is discernible from the evenness tester chart, and no periodic variation at an interval of 10 m or less exists in the diagram for analyzing the period of fiber size variation.
(Note the toughness is calculated from the equation of strength at breakxc3x97elongation at breakxc2xd (cN/dtex)%xc2xd, and a length of fiber to be measured by the evenness tester is 250 m.)
A second aspect of the present invention is a method for producing a fiber from PTT having an intrinsic viscosity in a range from 0.7 to 1.3, composed of 95 mol % or more of repeated units of trimethylene terephthalate and 5 mol % or less of those of other ester by a two-step method wherein an undrawn fiber is once taken up in a spinning process as a package form at a take-up rate of 1900 m/min or less and then drawn in a drawing process, characterized in that the undrawn fiber is taken up at a take-up tension in a range from 0.04 to 0.12 cN/dtex, and retained in an environmental atmosphere having a temperature in a range from 10 to 25xc2x0 C. and a relative humidity in a range from 75 to 100% during a winding process, a storage process and a drawing process, and in that the drawing of the undrawn fiber is completed within 100 hours after the undrawn fiber has been taken up.
The present invention will be described in more detail below.
The present invention is a method for producing a fiber from PTT having an intrinsic viscosity in a range from 0.7 to 1.3, composed of 95 mol % or more of repeated units of trimethylene terephthalate and 5 mol % or less of those of other ester by a two-step method wherein an undrawn fiber is once taken up in a spinning process as a package form at a take-up rate of 1900 m/min or less and then drawn in a drawing process, and a twisted or non-twisted PTT filament fiber obtained by the above method.
In general, the drawing operation in the two-step method is carried out by a so-called draw twister shown in FIG. 7 or a draw winder shown in FIG. 8, and a drawn fiber is wound as a pirn (shown in FIG. 9) in the former or as a cheese (shown in FIG. 10) in the latter. Generally speaking, the fiber wound in the pirn is twisted, while the fiber wound in the cheese is non-twisted. In FIGS. 7 and 8, reference numeral 15 denotes an undrawn package, 16 a supply roll, 17 a hot plate, 18 a draw roll, 19 a pirn and 20 a cheese. Also, in FIG. 9, reference numerals 21 and 22 denote a bobbin and a drawn fiber, respectively. In FIG. 10, reference numerals 23 and 24 denote a paper tube and a drawn fiber, respectively.
In the first aspect of the present invention, the toughness is 19 (cN/dtex)%xc2xd or more. If the toughness is less than 19 (cN/dtex)%xc2xd, mechanical properties such as a tearing strength of a knit or woven fabric obtained by processing the PTT fiber becomes too inferior to be used for clothing. A preferable value of the toughness is 21 (cN/dtex)%xc2xd or more. In this regard, the toughness of polyethylene terephthalate fiber for general clothing use is approximately 24 (cN/dtex)%xc2xd.
In the first aspect of the present invention, a variation value of fiber size (U%) during the continuous measurement of the fiber size by an evenness tester is 1.5% or less. If the U% exceeds 1.5%, physical properties of the fiber become uneven to result in a streaky or irregularly dyed knit or woven fabric. U% is preferably 1.2% or less, more preferably 1.0% or less.
It is thought that the undrawn fiber obtained under conditions wherein a package of the undrawn fiber is significantly transformed due to the shrinkage with time has a large variation in size of undrawn fiber to worsen the U%.
According to the first aspect of the present invention, there is a periodic variation on a smaller fiber size side at an interval of 10 m or less on a chart obtained by the continuous measurement of a fiber size by an evenness tester, and a magnitude of the variation is 2% or less relative to an average fiber size. This corresponds to the above-mentioned requisite (1).
The confirmation of whether or not the periodicity exists in the variation of fiber size may be possible by directly reading a chart of the continuous measurement of fiber size (Diagram Mass) or through an analysis of the periodic variation in fiber size (Spectrogram Mass) described later. In the latter, if there is a peak in CV value representing a variance of the fiber size (shown in a vertical axis of the analysis diagram) exceeding approximately 0.2% between 1 m and 10 m of a length of period (shown in a horizontal axis of the analysis diagram), it is said that the periodicity exists in the variation of fiber size.
The periodic variation on the smaller fiber size side is a variation corresponding to downward whisker-like signals generating at an equal interval on a continuous measurement chart of fiber size shown in FIG. 4A. A fact that the signals generated at an equal interval are observed at the equal interval means that the fluctuation of fiber size causing the signals periodically occurs, and the existence of a downward signal means that a fiber size (a fineness of fiber) at that point as seen in the lengthwise direction of the fiber varies to a smaller side. A ratio of the periodic variation on a smaller fiber size side relative to the average fiber size is directly readable from the chart. If this ratio exceeds 2%, a knit or woven fabric suitable for a clothing use is not obtainable from this fiber even though the U% is 1.5% or less, because the dyeing speck and the unevenness of luster become significant due to this periodic variation of fiber size.
An interval of the period variation of fiber size substantially corresponds to a product of one traverse stroke or two between opposite ends of an undrawn fiber package and a draw ratio. It is surmised that a length of undrawn fiber existing at opposite ends or one end of the package is drawn due to the unwinding resistance to cause the periodic variation of fiber size on the smaller fiber size side. In the two-step method, the interval of the periodic variation of fiber size is determined by a traverse stroke, a winding angle and a draw ratio of a winder for the undrawn fiber and, in general, is 10 m or less.
When the periodic variation of fiber size on the smaller fiber size side becomes small, the downward signals generated at the equal pitch are not discernible on the continuous measurement chart of fiber size as shown in FIG. 4B. However, in a period analysis diagram (shown in FIG. 5B) corresponding to FIG. 4B, there are signals representing the existence of the periodic variation. The above-mentioned requisite (2) defines such a phenomenon that signals are not discernible in the chart but are represented in the period analysis diagram. In the diagram shown in FIG. 5B, four signals, i.e., those projecting like mountains exist in an area of the horizontal axis shorter than 10 m. This state, wherein one mountain-like signal, or more, is visible, is a state wherein the periodic variation exists in fiber size on the period analysis diagram as defined in the requisite (2). In this regard, according to the period analysis, it could not be determined whether or not the signals belong to the smaller fiber size side or the larger fiber size side. The range satisfying the requisite (2) is a favorable range of the present invention.
If the periodic variation of fiber size becomes further smaller, no mountain-like signal is visible even in the periodic analysis diagram. This state is one showing the characteristic of the requisite (3). That is, the range satisfying the requisite (3) is a more favorable range of the present invention.
In the second aspect of the present invention, a winding tension of the undrawn fiber in the spinning process is 0.04 to 0.12 cN/dtex. If the winding tension is within this range, no significant transformation of the package results even though the undrawn fiber slightly contracts with time. If the atmospheric temperature is retained at a relatively high value within a range defined by the present invention, the winding tension is preferably set at a relatively low level. On the other hand, if the atmospheric temperature is retained at a relatively low value, the winding tension is preferably set at a relatively high level.
If the winding tension is less than 0.04 cN/dtex, it becomes difficult to wind up the undrawn fiber continuously because the fiber runs unstably. If the winding tension exceeds 0.12 cN/dtex, the transformation of the package is not avoidable due to the shrinkage of the undrawn fiber with time even though the environmental atmospheric temperature is retained in a range from 10 to 25xc2x0 C.
According to the second aspect of the present invention, the winding, storage and drawing processes of the undrawn fiber are retained in the environmental atmosphere having a temperature in a range from 10 to 25xc2x0 C. and a relative humidity in a range from 75 to 100%.
If the atmospheric temperature is lower than 10xc2x0 C., the shrinkage of the undrawn fiber with time becomes extremely small, but the cost necessary for the temperature control increases as well as the working efficiency lowers due to the cold. On the contrary, if the atmospheric temperature exceeds 25xc2x0 C., the shrinkage of the undrawn fiber with time becomes so large that the transformation of the package is not avoidable even though the winding tension is lowered to 0.04 cN/dtex.
A favorable range of the atmospheric temperature is from 15 to 22xc2x0 C. in view of the transformation of the undrawn fiber package, the cost necessary for temperature control and the working efficiency.
In the second aspect of the present invention, the relative humidity of the atmosphere in which the undrawn fiber is retained during the respective processes is in a range from 75 to 100%. If the relative humidity is less than 75%, water imparted together with a finishing agent to the undrawn fiber package is promptly evaporated solely at the opposite ends of the package to lower the moisture content of the undrawn fiber in these portions, which results in the generation of much fluff in the drawn fiber as well as the rise in U% of the fiber exceeding 1.5% after being drawn whereby the unevenness or the streaky defect are significant in the dyed fabric. A more favorable range of the relative humidity is from 80 to 95%.
According to the second aspect of the present invention, it is necessary to complete the drawing of the undrawn fiber within 100 hours after the winding. The time from the initiation of the winding process to the completion of the drawing process, that is, a period from an instant at which a leading end of the undrawn fiber is wound at the innermost layer of the undrawn fiber package to an instant at which the leading end is drawn, is generally referred to as a lag time. The lag time must be within 100 hours in the present invention.
If the lag time exceeds 100 hours, water imparted to the undrawn fiber together with the finishing agent is partly evaporated to make the water content of the respective portions of the package unequal, while the shrinkage of the undrawn fiber with time is small to minimize the package transformation, whereby the U% of the drawn fiber becomes larger than 1.5% to result in the dyeing speck (the dyeing grade is lowered below a reject level). The lag time is preferably within 75 hours, more preferably within 50 hours.
A detailed description will be given for PTT polymer according to the present invention.
PTT according to the present invention is composed of 95 mol % or more of repeated units of trimethylene terephthalate and 5 mol % or less of those of other ester.
That is, the PTT according to the present invention is a copolymer composed of PTT homopolymer and other ester units of 5 mol % or less. A representative of the copolymer components is as follows:
An acidic component includes dicarbonic acid having sulfonic group, represented by 5-sodium sulfoisophthalic acid, and metallic salts thereof; aromatic dicarbonic acid represented by isophthalic acid; aliphatic dicarbonic acid represented by adipic acid, while a glycolic component includes ethylene glycol, butylene glycol and polyethylene glycol. A plurality of copolymeric components may be contained.
An intrinsic viscosity of PTT according to the present invention is in a range from 0.7 to 1.3. For a clothing use, a preferable range is from 0.8 to 1.1.
PTT according to the present invention may contain additives, such as a residual metal-type catalyst, a heat stabilizer, an antioxidant, a delusterant, a shade adjuster, a flame retardant, an ultraviolet inhibitor or others, which may be contained as copolymerized components.
A known method may be applied to produce PTT according to the present invention. In general, after being polymerized in a molten state, an intrinsic viscosity of the polymer may be further increased through the solid-phase polymerization.
In the production of PTT fiber according to the present invention, for example, a process shown in FIGS. 6 and 7 may be adopted.
In FIG. 6, PTT pellets dried in a dryer 3 to have a moisture content of 30 ppm or less is supplied to an extruder 4 set at a temperature in a range from 255 to 265xc2x0 C. and melted therein. The molten PTT is fed through a bend 5 to a spin head 6 set at a temperature in a range from 250 to 265xc2x0 C. and metered by a gear pump. Thereafter, PTT is extruded into a spinning chamber as a multifilament 9 through a spinneret 8 having a plurality of orifices and mounted to a spin pack 7.
An optimum temperature is selected from the above range as that of the extruder or the spin head in accordance with an intrinsic viscosity and a shape of the PTT pellet.
The PTT multifilament extruded into the spinning chamber is thinned by godet rolls 12, 13 rotating at predetermined speeds, while being quenched by a cooling air 10 to a room temperature, and solidified to be an undrawn fiber having a predetermined fiber size. Prior to being in contact with the godet roll 12, the undrawn fiber is imparted with a finishing agent by a finishing agent applicator 11. After departing from the godet roll 13, the undrawn fiber is taken up by a winder 14 to be an undrawn fiber package. A winding speed of the undrawn fiber is preferably in a range from 1000 to 1900 m/min.
In this process, an environmental atmosphere surrounding the godet rolls 12, 13 and the winder is maintained at a temperature in a range from 10 to 25xc2x0 C. and a relative humidity in a range from 75 to 100%. Also, when it is necessary to temporarily store the undrawn fiber package thus formed prior to being delivered to a drawing process, the package is stored in the atmosphere with the above-mentioned conditions.
A winding tension of the undrawn fiber is adjustable by changing the winding speed; i.e., a ratio of the peripheral speed of the undrawn fiber package to that of the godet roll 13 during the winding operation.
The finishing agent is of an aqueous emulsion type which is safe for the working environment. A concentration of the finishing agent is preferably in a range from 10 to 30 wt %. When the aqueous emulsion type finishing agent is imparted, the undrawn fiber after being wound contains an amount of water in accordance with the concentration and the adhesion degree of the finishing agent. The moisture content is generally in a range from 3 to 5 wt %.
The undrawn fiber package is then delivered to a drawing process in which it is drawn by the draw twister as shown in FIG. 7. The undrawn fiber package 15 is retained in the atmosphere of the draw twister at a temperature in a range from 10 to 25xc2x0 C. and a relative humidity in a range from 75 to 100% while being drawn. In the draw twister, the undrawn fiber 15 is first heated on the supply roll 16 having a temperature in a range from 45 to 65xc2x0 C. and drawn by using a ratio of the peripheral speed of the draw roll 18 to that of the supply roll 16 to have a predetermined fiber size. The fiber runs during or after the drawing while being in contact with the hot plate 17 set at a temperature in a range from 100 to 150xc2x0 C. to be subjected to a stretch heat treatment. The fiber exiting the draw roll is twisted by a spindle and wound to form the pirn 19.
In the above process, the ratio of the peripheral speed of the draw roll 18 to that of the supply roll 16, that is, the draw ratio, and the hot plate temperature are preferably set so that the drawing tension is approximately 0.35 cN/dtex.